Embodiments herein generally relate to printing methods and printing systems that utilize transfer assist blades, and more particularly to methods and systems that vary the pressure supplied by the transfer assist blade as a sheet of media passes between the transfer assist blade and the photoconductor.
Often, it is desirable to have printing devices perform printing all the way to the edge of the sheet of media that is being printed on. This is commonly referred to as “print-to-edge” activity. However, print-to-edge performance is a very challenging aspect of printing, especially at the leading edge portion (LE) and trailing edge portion (TE) of the media where the transfer of toner from the photoreceptor (PR) to the media may be influenced by other factors such as reverse biasing in bias transfer belt (BTB) systems or transfer assist blade (TAB) blanking in Corotron/TAB (CTAB) systems. The reason for this is because many printing engines use the spaces between the sheets (interdocument zone or IDZ) to print toner patches used by the various control systems to steer image quality (IQ). Such toner patches are not meant to be transferred or cleaned in this step of the process and, therefore, should be left intact to prevent undesired contamination.
In corotron/TAB systems transfer assist blade blanking is not 100% effective at the leading edge portion and trailing edge portion of the prints due to dependencies on transfer assist blade material dynamic response and the transfer assist blade linkage's inability to react quickly. This issue is aggravated by stress conditions such and wet environment and media conditions, and low stiffness of lightweight media. Sometimes, a 3 mm border is provided around the printing area to safeguard this shortfall; however, questionable performance can still occur in stressful or extreme conditions in an area up to 15 mm from the media edge. Another issue is trail edge flip (TEF) which is a defect band that can occur approximately 45 mm from the trailing edge portion. Trail edge flip affects mainly heavyweight media.
In view of these issues, the embodiments herein provide transfer pressure switching or transfer assist blade switching (in Corotron/TAB systems) to enable print-to-edge performance (0-10 mm from each edge, up to 15 mm in very extreme conditions). This function is achieved by enabling the transfer assist blade to switch from a normal pressure (desired media body pressure, normal state today) to a higher pressure in the trailing edge portion and leading edge portion (20-30% higher pressure) and down to zero pressure (or blanking) in the inter-document zone (to leave the process control patches unaffected). The embodiments herein also extend the trailing edge portion timing flexibility to eradicate trailing edge portion flip (which can occur 45 mm from trailing edge portion).
One exemplary printing apparatus herein includes a charging device positioned adjacent a photoreceptor that places a latent image charge on the photoreceptor. A donor device is adjacent the photoreceptor, and transfers marking material to regions of the photoreceptor that have received the latent image charge. In addition, a media path that is adjacent the photoreceptor places at least one sheet of media on the photoreceptor and the marking material.
A transfer assist blade, that is also adjacent the photoreceptor, presses the sheet of media against the photoreceptor to cause the marking material to be transferred to the sheet of media. Thus, the transfer assist blade applies pressure to push the sheet of media against the photoreceptor when the photoreceptor moves the sheet of media by the transfer assist blade. The transfer assist blade retracts from the photoreceptor after the sheet of media has passed by the transfer assist blade such that the transfer assist blade does not contact the photoreceptor in regions where the photoreceptor is exposed between adjacent sheets of media.
The apparatus also includes a controller that is operatively connected to the transfer assist blade. The controller causes the transfer assist blade to apply more pressure to leading and trailing portions of the sheet of media relative to the middle portion of the sheet of media. The controller causes the transfer assist blade to apply at least 20% greater pressure to the leading and trailing portions relative to the middle portion of the sheet of media. Also, the additional pressure is applied up to approximately 15 mm of the leading edge portion of the sheet of media and is applied up to approximately 60 mm of the trailing edge portion of the sheet of media.
The embodiments herein also include computer storage media and method embodiments. One such method embodiment places at least one sheet of media on a photoreceptor and moves the sheet of media by the transfer assist blade using the photoreceptor while the transfer assist blade applies pressure to push the sheet of media against the photoreceptor. The method causes the transfer assist blade to apply more pressure to leading and trailing portions of the sheet of media relative to a middle portion of the sheet of media using a controller. The method retracts the transfer assist blade from the photoreceptor after the sheet of media has passed by the transfer assist blade so that the transfer assist blade does not contact the photoreceptor in inter-document regions (zones) where the photoreceptor is exposed between adjacent sheets of media.
These and other features are described in, or are apparent from, the following detailed description.